Relaxin is a small peptide hormone primarily produced by the ovaries and placenta during pregnancy (Sherwood (2004) Endocr Rev 25, 205-234). Three relaxin genes have been identified in humans, designated as H1, H2, and H3 relaxin. H2 relaxin is the major circulating relaxin that is substantially increased during pregnancy (Sherwood (1994) In The Physiology of Reproduction (Knobil, E., and Neill, J. D., eds) Vol. 1 pp. 861-1009). H2 relaxin binds to relaxin family peptide receptor 1 (RXFP1, previously known as LGR7) with high affinity (Bathgate et al., (2006) Pharmacol Rev 58, 7-31). A growing amount of literature suggests that relaxin has extensive cardiovascular effects even outside of pregnancy, such as promoting vasodilation and angiogenesis, and protecting against fibrosis and inflammation in systemic and renal circulations (Bani, (2008) Vasc Health Risk Manag 4, 515-524; Conrad et al. (2004) Am J Physiol Regul Integr Comp Physiol 287, R250-261). Recently, the therapeutic potential of relaxin has been suggested for treatment of heart failure and preeclampsia (Teerlink et al., (2009) Lancet 373, 1429-1439; Unemori et al., (2009) Ann N Y Acad Sci 1160, 381-384).